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Old 26th October 2004, 09:26 PM   #1
Hesky is offline Hesky  United Kingdom
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Default VSE riaa equalizer phono stage

Hi all,

Has anyone had any experience with the Vacuum State Electronics FVP5A phono stage? The input impedance of my pre-amp is 50k so I though the riaa stage would be pretty compatible (leave out the line stage).
My initial idea was to use a smooth non regulated B+ supply as the current draw would be pretty low. Is this "SuperReg" a specific design or just a 250v regulated supply?

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Hesky
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Old 27th October 2004, 12:07 AM   #2
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Hi,

Quote:
The input impedance of my pre-amp is 50k so I though the riaa stage would be pretty compatible (leave out the line stage).
That should work fine but read the note on the schematic warning against some attenuators.

Quote:
Is this "SuperReg" a specific design or just a 250v regulated supply?
It is not specific to the phonopreamp you want to build but is fully explained in AWs Tube Preamp Cookbook.

Cheers,
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Old 27th October 2004, 12:58 AM   #3
Hesky is offline Hesky  United Kingdom
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Hi frank,

Quote:
That should work fine but read the note on the schematic warning against some attenuators.
I noticed that, my home made pre-amp uses an alps blue pot so it shouldn’t be a problem.

I think I should "take my stabilizes off" so to speak and design my own regulated b+ supply for this phono stage.

I'd like to design my own phono stage, but I'm not confident (smart is a more appropriate word) enough to tackle the calculations required to select values for an riaa circuit, not yet anyway.

Thanks
Hesky
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Old 27th October 2004, 02:20 AM   #4
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This circuit is a cascode input in which the fet replaces the traditional bottom triode. If you want to stay "all tube", you might look at this Steve Bench design. I haven't heard Mr. Wright's design, but Mr. Bench's definately rocked my boat.

It also needs a regulated(quiet) psu.

You can't go wrong either way.
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Old 27th October 2004, 06:10 PM   #5
Hesky is offline Hesky  United Kingdom
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Hi Pedro,

Thanks for the link to Steve's phono design, I navigated my way around to his site and its a real interesting read!! He's attempted five phono designs and really rates the one you linked.
I'm very tempted.

It sounds like you have already built one of his phono designs.

Thanks
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Old 27th October 2004, 06:17 PM   #6
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Quote:
Originally posted by Hesky

It sounds like you have already built one of his phono designs.

Thanks
Yep, that's the one that I built. It's easily the best phono stage that I've ever owned.

As far as Mr. Wright's stage, I think Brett, who posts on this forum, has built it - and really likes it.
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Old 27th October 2004, 06:39 PM   #7
Hesky is offline Hesky  United Kingdom
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Hi Pedro,
What sort of B+ supply did you use? regulated or a real smooth non regulated suppy.
He says the circuit can run from anything from 170 volts to 250 volts. 250 volts gives a bit more gain and a little less distortion. The downside is it consumes more current, which isnt much of a problem.

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Old 27th October 2004, 06:54 PM   #8
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Quote:
Originally posted by Hesky
Hi Pedro,
What sort of B+ supply did you use? regulated or a real smooth non regulated suppy.
He says the circuit can run from anything from 170 volts to 250 volts. 250 volts gives a bit more gain and a little less distortion. The downside is it consumes more current, which isnt much of a problem.

Cheers
I'm using 2 OC3's per channel for the phono stage. The output to the line stage has since dropped to ~250V since I changed over to 12B4A's.

here's the schematic:

Click the image to open in full size.
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Old 27th October 2004, 09:17 PM   #9
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Hesky,

I 've build the FVP5A and it's definite the best and most quiet MCphono stage I ever build.

The superreg is a special powersupply that I really recommend.
It makes the FVP really sing.

Dick.
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Old 27th October 2004, 11:56 PM   #10
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Quote:
The superreg is a special powersupply that I really recommend.
Hi dick, I was thinking about building my own regulated B+ supply based on the mje340 transistor and the 317t voltage regulator. maybe tube rectified.

Pedro, your B+ supply looks pretty sweet, cant help but think how hard it would be to get hold of those OC3 voltage regulator tubes!

Just a few questions, is it beneficial to also us an isolation transformer? and how exactly does the 10m45s current regulator and the OC3 voltage regulator work together, what are they doing moreover?

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